Stereomour II (in progress)

[denti alligator]

Well, I'm still waiting for it to ship, but I thought I'd start a thread anyway, since I want to ask about ohms. I'm using a pair of Klipsch Forte II horn speakers. I'm assuming I would want to wire the Stereomour for 8 ohms. Is that right?

This will be my first major upgrade since getting the S.E.X. 2.0 back in 2010 or so. I'm pretty excited. I think I will continue to use the S.E.X. as a headphone amp until I get some old B&W speakers set up upstairs, then I'll probably swap it out with my Crack in the main listening room. My plan is to use the Steremour switching capabilities and output to the Crack with a separate set of RCAs.

[Doc B.]

Have you looked up the nominal impedance of the Forte II?

[denti alligator]

Apparently:

 99dB sensitivity, 8 ohm nominal impedance, 4 ohm minimum

Then there's this file, which I don't quite know how to read:
https://community.klipsch.com/index.php?app=core&module=attach&section=attach&attach_id=97104

[Paul Joppa]

The dip to ~3.8 ohms in the deep bass worries me a little. I suggest you try it at 4 ohms as well as 8 ohms, and compare them.

[denti alligator]

Thanks, Paul. Can you explain why it worries you, and also what differences I should listen for?

[Paul Joppa]

It's the damping factor. Most speakers are designed to operate best with an amp that has a very high damping factor; SETs usually have a DF between 2 and 4. This makes the response sensitive to variations in speaker impedance. Peaks when the impedance is high are limited, but notches when the impedance is low are unbounded.

In the Forte II graph, the biggest dropout would be in the bass where it drops below half of the nominal 8 ohms. There will be a smaller peak in the upper midrange where the impedance is high. Room acoustics are significant, especially in the bass, so sometimes just moving the speaker around will adequately compensate. That's why I suggested trying both options and listening.

[denti alligator]

Arriving today! Will see about posting pics as I assemble.

[Sugar Man]

Good luck!  Fun build.

[denti alligator]

I'm terrible with a drill, and even though I marked where I wanted the extra RCA jacks, they ended up elsewhere. Oh well, they'll be mostly hidden anyway.

(http://i63.tinypic.com/116nqqu.jpg)

Made a little more progress. Slowly building. Using Danish Oil on base. More of that later.

(http://i63.tinypic.com/21cf7k1.jpg)

[denti alligator]

What am I allowed to do to the plate chokes? I painted mine on the SEX, but I'd like to keep them simple here. Can I clean them with something?

[Paul Birkeland]

You can burnish the steel channel frames with steel wool.  I wouldn't clean or treat any other part of the choke.

-PB

[denti alligator]

Ok, thanks. One more question ... I'm waiting for a replacement of the 3.3uF cap, one of which came damaged. Is there a voltage range that is acceptable if I wanted to use another 3.3uF cap in the meantime?

[Paul Birkeland]

630V or greater.

[denti alligator]

Thanks, and I'm assuming this cap can impact the sound quality, that is, if I go for "boutique" caps I should hear some difference?

[Jamier]

You will be amazed at how good it sounds with the Solens.The design of the circuit is more important than the parts that go into it.